[MuddyMules]

Actually the plate is correct in offset printing. A film negative is burned onto a printing plate which creates a positive image (as shown on the actual printed sheet). The ink goes to the plate and then is transferred to a rubber blanket and then transferred onto the press sheet.

In flexo printing, it would be opposite.

My guess is that the plate is too new for that era and was used as a reprint for the card.